Methods of forming silicon carbide semiconductor devices having buried silicon carbide conduction barrier layers therein

ABSTRACT

A silicon carbide semiconductor device includes a silicon carbide substrate, an active layer in the substrate and a silicon carbide buried layer which provides a conduction barrier between the substrate and at least a portion of the active layer. The buried layer is preferably formed by implanting second conductivity type dopants into the substrate so that a P-N junction barrier is provided between the active layer and the substrate. The buried layer may also be formed by implanting electrically inactive ions into the substrate so that a relatively high resistance barrier is provided between the active layer and the substrate. The electrically inactive ions are preferably selected from the group consisting of argon, neon, carbon and silicon, although other ions which are electrically inactive in silicon carbide may be used. The implantation of the electrically inactive ions is designed to cause the formation of a large number of electrically active deep level defects in the buried layer, particularly near the peak of the implant profile which is Gaussian in shape. These steps can be utilized in the formation of a variety of silicon carbide semiconductor devices such as lateral field effect devices and devices having both vertical and lateral active regions which are designed for high power applications. In particular, lateral silicon carbide-on-insulator enhancement and depletion mode field effect transistors (FETs) can be formed in accordance with the present invention. Vertical silicon carbide power MESFET devices can also be formed by incorporating a silicon carbide source region in the active layer at the first face of a silicon carbide substrate and a drain region at the second face and by providing a Schottky barrier gate electrode on the first face.

This application is a divisional of application Ser. No. 08/692,587,filed Aug. 6, 1996, now U.S. Pat. No. 5,681,762, which is a divisionalof parent application Ser. No. 08/337,977, filed on Nov. 14, 1994, nowU.S. Pat. No. 5,543,637, issued Aug. 6, 1996.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices and methods andmore particularly to silicon carbide semiconductor devices and methods.

BACKGROUND OF THE INVENTION

As is well known to those having skill in the art, monocrystallinesilicon carbide is particularly well suited for use in semiconductordevices, such as integrated circuit semiconductor devices and powersemiconductor devices. Integrated circuit semiconductor devicestypically include many active devices such as transistors in a singlesemiconductor substrate. Power semiconductor devices, which may beintegrated circuit devices, are semiconductor devices which carry largecurrents and/or support high voltages.

Silicon carbide has a wide bandgap, a high melting point, a lowdielectric constant, a high breakdown field strength, a high thermalconductivity and a high saturated electron drift velocity compared tosilicon, which is the most commonly used semiconductor material. Thesecharacteristics allow silicon carbide microelectronic devices to operateat higher temperatures and higher power levels than conventional siliconbased devices. In addition to the above advantages, silicon carbidepower devices can operate with lower specific on-resistance thanconventional silicon power devices. Some of the advantages of usingsilicon carbide for forming power semiconductor devices are described inarticles by K. Shenai, R. S. Scott and inventor B. J. Baliga, entitledOptimum Semiconductors for High-Power Electronics, IEEE Transactions onElectron Devices, Vol. 36, No. 9, pp. 1811-1823 (1989); and by M.Bhatnagar and inventor B. J. Baliga entitled Analysis of Silicon CarbidePower Device Performance, ISPSD '91, Abstr. 8.3, pp 176-180 (1991).

In particular, semiconductor devices such as silicon carbide powerMOSFETs have been considered attractive candidates for high powerapplications because the resistance of the MOSFET drift region is 200times smaller than that for silicon devices with the same breakdownvoltage. However, the operation of some silicon carbide power devicesmay require the formation of an inversion layer channel when turned on.This is unfortunate because the inversion layer mobility measured forelectron inversion layers has been found to be relatively small (˜15 cm²V⁻¹ sec⁻¹). This will result in a relatively large channel resistancewhich can degrade performance of the silicon carbide power device. Thus,notwithstanding the benefits of using silicon carbide as a semiconductormaterial, there continues to be a need for silicon carbide semiconductordevices which do not require the formation of inversion layer channelswhen turned on. Examples of such devices are disclosed in U.S. Pat. Nos.5,323,040, and 5,396,085 to Baliga, entitled Silicon Carbide FieldEffect Device and Silicon Carbide Switching Device With Rectifying Gate,the disclosures of which are incorporated herein by reference. Thesedevices may, however, require the formation of vertically walledtrenches in silicon carbide and relatively high resolution lithographicsteps during processing, which makes these devices difficult and/orexpensive to produce.

Many of the methods for forming semiconductor devices also require theformation of insulating regions, such as oxides, that act as masks fordevice processing, perform the function of electrically isolating one ormore regions of a semiconductor device as well as isolating adjacentdevices on a semiconductor substrate. Conventional techniques forforming insulating regions on silicon include thermal oxidation, lowpressure chemical vapor deposition (LPCVD) and plasma-assisteddeposition. As will be understood by one skilled in the art, thermaloxidation is probably the most common technique used to grow highquality oxides, such as those made of SiO₂, on silicon substrates. SIMOXtechniques have also been successfully used to form silicon SOIsubstrates.

Notwithstanding these attempts at growing insulating regions in silicon,however, similar techniques have not found substantial application inthe formation of insulating regions in silicon carbide devices. This isparticularly true with respect to the formation of relatively thickinsulating regions. As will be understood by those skilled in the art,thick insulating regions are particularly important for silicon carbidepower devices in order to inhibit leakage currents, electric arcing, orfield oxide breakdown, when such devices are operated in the presence ofhigh electric fields and/or at high current levels. Thus, therecontinues to be a need for a method of forming silicon carbide deviceswhich have insulating regions therein that provide electrical isolationand inhibit leakage currents.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide improvedsilicon carbide semiconductor devices which can be operated withoutrequiring the formation of an inversion layer channel, and methods offabricating same.

It is another object of the present invention to provide silicon carbidesemiconductor devices for high power applications, and methods offabricating same.

It is still another object of the present invention to provide siliconcarbide semiconductor devices which are suitable for large scaleintegration on a semiconductor substrate, and methods of fabricatingsame.

It is a further object of the present invention to provide siliconcarbide semiconductor devices which include insulating regions thereinfor providing electrical isolation, and methods of fabricating same.

These and other objects are provided, according to the presentinvention, by a semiconductor device having a silicon carbide substrate,a semiconducting silicon carbide active layer in the substrate and asilicon carbide buried layer which provides a conduction barrier betweenthe silicon carbide substrate and at least a portion of the siliconcarbide active layer. According to one aspect of the present invention,the silicon carbide buried layer is formed by implanting secondconductivity type dopants into a silicon carbide substrate of firstconductivity type so that a P-N junction barrier is provided between thesilicon carbide active layer and the substrate. This barrier can then beused in the formation of power semiconductor devices which have bothlateral and vertical active regions and which can be operated withoutthe formation of an inversion layer. According to another aspect of thepresent invention, the silicon carbide buried layer is formed byimplanting electrically inactive ions into the silicon carbide substrateso that a relatively high resistance barrier is provided between thesilicon carbide active layer and the substrate. The electricallyinactive ions are preferably selected from the group consisting ofargon, neon, carbon and silicon, although other ions which areelectrically inactive in silicon carbide may be used. This highresistance barrier can then be used to provide electrical isolation to asemiconductor device and perform other insulating functions.

In particular, one embodiment of a semiconductor device according to thepresent invention includes a silicon carbide buried layer which isformed by implanting electrically inactive ions into a silicon carbidesubstrate of first conductivity type so that the buried layer containsboth first conductivity type dopants and the implanted electricallyinactive ions therein. The implantation step is designed to cause theformation of a large number of electrically active deep level defects inthe buried layer, particularly near the peak of the implant profilewhich is Gaussian in shape. These electrically active defects are causedby the presence of the implanted electrically inactive ions atinterstitial locations of the silicon carbide lattice. Moreover, thepresence of ions such as neon or argon at substitutional locations inthe silicon carbide lattice will also result in the formation ofelectrically active defects. To obtain a preferred number ofelectrically active defects, the inactive ions can be implanted atsufficiently high energies and doses. Such defects would typically beavoided in the design of conventional semiconductor devices, however,the present invention utilizes these defects to achieve desiredperformance characteristics. This is because the defects are used tocompensate for the first conductivity type dopants in the implantedregion.

These compensation effects cause the extrinsic Fermi level (ε_(fe)) inthe implanted region to move towards its intrinsic Fermi level (ε_(fi)).The implanted region therefore acquires electrical characteristics thatare similar to intrinsic silicon carbide. Intrinsic silicon carbide canbe used as a high resistance conduction barrier because of therelatively large bandgap between silicon carbide's intrinsic Fermi level(ε_(fi)) and its conduction or valence band edge (E_(c), E_(v)). Forexample, the resistivity of intrinsic silicon carbide has been estimatedto be 7×10⁹, 5×10¹⁴ and 2×10¹⁶ Ohm-cm for 3C-SiC, 6H-SiC and 4H-SiCpolytypes, respectively. The compensation effects caused by theimplantation of electrically inactive ions can also be advantageouslyused to form a silicon carbide-on-insulator substrate having a buriedelectrically insulating layer. This buried layer also has electricalproperties similar to intrinsic silicon carbide. This aspect of thepresent invention would be difficult to achieve in conventionalsemiconductor materials such as silicon, germanium and gallium arsenidebecause these materials have relatively low resistivities as intrinsicsemiconductors.

Another embodiment of a semiconductor device according to the presentinvention includes a silicon carbide substrate of first conductivitytype, having first and second opposing faces, and a silicon carbideburied layer which has second conductivity type dopants therein and anopening therethrough. A silicon carbide active layer of firstconductivity type, which has relatively few second conductivity typedopants therein, is also provided between the buried layer and the firstface of the substrate. The silicon carbide active layer can also have afirst conductivity type doping concentration greater than that of thesubstrate. A substrate connecting region of first conductivity type isalso provided in the opening so that charge carriers in the active layercan be transferred to the substrate and vice versa. According to thisembodiment, the silicon carbide buried layer is compensated by theimplanted second conductivity type dopants and the silicon carbideactive layer is also compensated by the second conductivity typedopants, although to a significantly lesser extent. The compensation inthe silicon carbide active layer is sufficient, however, so that themagnitude of the difference in energy between the Fermi level of thesilicon carbide active layer and the Fermi level of intrinsic siliconcarbide is less than the magnitude of the difference in energy betweenthe Fermi level of the substrate connecting region and the Fermi levelof intrinsic silicon carbide, even though both the active layer and thesubstrate connecting region are of the same net conductivity type. Thisembodiment can also include electrically inactive ions in place of thesecond conductivity type ions.

These aspects of the present invention can be utilized in the formationof a variety of silicon carbide semiconductor devices such as lateralfield effect devices and devices having both vertical and lateral activeregions which are designed for high power applications. In particular,lateral silicon carbide-on-insulator enhancement and depletion modefield effect transistors (FETS) can be formed in accordance with thepresent invention. Vertical silicon carbide power MESFET devices canalso be formed by incorporating a silicon carbide source region adjacentthe first face and a drain region adjacent the second face, and byproviding a Schottky barrier gate electrode on the first face, above thesubstrate connecting region. This vertical MESFET can also be operatedwithout requiring the formation of an inversion layer channel. It willbe appreciated by those skilled in the art that other semiconductordevices can also incorporate the above described preferred aspects ofthe present invention.

Accordingly, the silicon carbide devices according to the presentinvention include a buried silicon carbide conduction barrier layerwhich provides electrical isolation between one or more regions of adevice or between adjacent devices in a substrate. The buried layer canbe formed by implanting electrically inactive ions or by implantingelectrically active ions which are of opposite conductivity typerelative to the substrate. The buried layer can then be patterned sothat the silicon carbide device does not require the formation of aninversion layer channel when turned on. The buried layer can also beused to isolate a device from an underlying silicon carbide substrate.The methods for forming the silicon carbide devices according to thepresent invention also do not require vertical processing or highresolution lithography steps, which makes the methods suitable for largescale processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-c are cross-sectional views of intermediate structures whichillustrate a method of forming a silicon carbide semiconductor deviceunit cell according to the present invention.

FIG. 2 illustrates a layout of a vertical MESFET integrated circuitaccording to the present invention.

FIG. 3a illustrates a silicon carbide-on-insulatormetal-oxide-semiconductor field effect transistor (MOSFET) according tothe present invention.

FIG. 3b illustrates a silicon carbide-on-insulatormetal-epitaxial-semiconductor field effect transistor (MESFET) accordingto the present invention.

FIGS. 4a-b illustrate implant distribution profiles for helium (He) andcarbon (C) in a silicon carbide substrate, respectively.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the thickness of layers and regions are exaggerated forclarity. Like numbers refer to like elements throughout.

Referring now to FIGS. 1a-c, a method of forming a silicon carbidesemiconductor device unit cell according to the present invention willbe described. The method begins with the steps of providing a siliconcarbide substrate 12 of first conductivity type (shown as N) havingfirst and second opposing faces 1a-b and then patterning a photoresistmasking layer 14 on the first face 12a to expose a portion thereof. Thisis then followed by the step of implanting ions 16 into the exposedportion of the face 12a so that a silicon carbide buried layer 18containing the implanted ions is formed. The silicon carbide buriedlayer 18 also contains the background first conductivity type dopants ofthe substrate. These ions 16 can be electrically inactive ions selectedfrom the group consisting of argon, neon, carbon and silicon. These ions16 can also be electrically active ions of second conductivity type suchas those selected from the group consisting of boron and aluminum asP-type dopants or nitrogen as an N-type dopant. Relatively thick buriedlayers can also be formed by performing multiple implant steps with thesame or different ions at the same or different energies and doselevels. The dose levels can also be sufficiently high to produce anamorphous silicon carbide buried layer 18.

Because the width ("W") of the buried layer 18 will be large compared tothe depth of the implanted ions 16, the distribution of the implantedions 16 in the substrate 12, taken along line A-A', can be approximatedas a one-dimensional Gaussian distribution of the form: ##EQU1## whereI(d) (cm⁻³) is the concentration of implanted ions 16. As illustrated byEquation (1), I(d) is a function of the distance "d" from the first face12a, the implant dose "D₀ " (cm⁻²), the depth of the peak of the implantdistribution "d_(P) " and the standard deviation of the implantdistribution "Δd_(P) ". Table 1 below illustrates preferred implantparameters for the above described electrically active and inactive ionsin 6H-SiC. As will be understood by those skilled in the art, the peakof the implant distribution d_(P) is a function of, among other things,the ion implant energy "E", the implant angle "∠" relative to the face12a and the crystallographic structure of the substrate 12 (e.g.,3C-SiC, 6H-SiC and 4H-SiC).

The implantation of the ions 16 also defines a semiconducting activelayer 15 between the buried layer 18 and the first face 12a. The activelayer 15 contains first conductivity type dopants and a relatively smallpercentage of the implanted ions 16 therein which are included in the"tail" of the implant distribution. Accordingly, the width of the buriedlayer "d₂ " equals two times the difference between the depth of thepeak of the implant distribution d_(P) and the thickness of the activelayer 15 "d₁ " (i.e., d₂ =2(d_(p) -d₁)). As defined herein, d₁ is thedistance "d" at which I(d) equals the doping concentration of thesubstrate (N_(d) or N_(a)), for d<d_(P). Thus, the concentration of theimplanted ions 16 in the active layer 15 can be significantly below thepeak concentration of implanted ions 16 in the buried layer 18, so thatthe active layer 15 is not significantly compensated by the implantedions 16. Moreover, the thickness of the active layer 15 (d₁) can beoptimally chosen for a particular device application by adjusting thedose and energy of the implanted ions 16.

In the case of the electrically inactive ions, the implantation step isdesigned to cause the formation of a large number of electrically activedeep level defects in the buried layer. These electrically activedefects are typically caused by the presence of the implantedelectrically inactive ions at interstitial locations of the siliconcarbide lattice. Moreover, the presence of ions such as neon or argon atsubstitutional locations in the silicon carbide lattice will also resultin the formation of electrically active defects. To obtain a preferrednumber of electrically active defects, the inactive ions can beimplanted at sufficiently high energies and doses. Such defects wouldtypically be avoided in the design of conventional semiconductordevices, however, the present invention utilizes these defects toachieve desired performance characteristics. This is because the defectsare used to compensate for the first conductivity type dopants in theimplanted region.

These compensation effects cause the extrinsic Fermi level (ε_(fe)) inthe implanted region to move towards its intrinsic Fermi level (ε_(fi)).The implanted region therefore acquires electrical characteristics thatare similar to intrinsic silicon carbide. Intrinsic silicon carbide canbe used as a high resistance conduction barrier because of therelatively large bandgap between silicon carbide's intrinsic Fermi level(ε_(fi)) and its conduction or valence band edge (E_(c), E_(v)). Forexample, the resistivity of intrinsic silicon carbide has been estimatedto be 7×10⁹, 5×10¹⁴ and 2×10¹⁶ Ohm-cm for 3C-SiC, 6H-SiC and 4H-SiCpolytypes, respectively. This aspect of the present invention would bedifficult to achieve in conventional semiconductor materials such assilicon, germanium and gallium arsenide because these materials haverelatively low resistivities as intrinsic semiconductors.

According to a preferred aspect of the present invention, the dose ofthe implanted electrically inactive ions 16 is chosen so that themagnitude of the difference in energy between the Fermi level of thesilicon carbide buried layer 18 and the Fermi level of intrinsic siliconcarbide (ε_(fi)) is less than the magnitude of the difference in energybetween the Fermi level of the silicon carbide substrate 15 and theFermi level of intrinsic silicon carbide. The dose level can also bechosen so that the buried layer 18 is an electrically insulating layerhaving a resistivity greater than 10⁹ Ohm-cm. Similarly, the siliconcarbide active layer 15 also contains the electrically inactive ions 16in sufficient quantity so that the magnitude of the difference in energybetween the Fermi level of the silicon carbide active layer 15 and theFermi level of intrinsic silicon carbide is less than the magnitude ofthe difference in energy between the Fermi level of the silicon carbidesubstrate 12 and the Fermi level of intrinsic silicon carbide.

                  TABLE 1                                                         ______________________________________                                                            ENER-                                                                         GY    d.sub.p                                                                            Δd.sub.p                                                                     I(d.sub.p)                                                                           d.sub.1                                                                            d.sub.2                       ION  D.sub.0 (cm.sup.-2)                                                                    ∠                                                                             (keV) (μm)                                                                            (μm)                                                                            (cm.sup.-3)                                                                          (μm)                                                                            (μm)                       ______________________________________                                        Ar   7 × 10.sup.13                                                                    9°                                                                           400   0.29 0.07 4 × 10.sup.18                                                                  0.10 0.43                          Ne   3 × 10.sup.14                                                                    9°                                                                           400   0.49 0.09 1 × 10.sup.19                                                                  0.16 0.60                          C    1.2 × 10.sup.15                                                                  9°                                                                           400   0.70 0.10 7 × 10.sup.19                                                                  0.31 0.74                          Si   1.3 × 10.sup.14                                                                  9°                                                                           400   0.36 0.08 8 × 10.sup.18                                                                  0.08 0.50                          B    1.8 × 10.sup.15                                                                  9°                                                                           400   0.81 0.1  9 × 10.sup.19                                                                  0.35 0.8                           Al   1.6 × 10.sup.14                                                                  9°                                                                           400   0.39 0.08 1 × 10.sup.19                                                                  0.08 0.55                          N    8 × 10.sup.14                                                                    9°                                                                           400   0.63 0.09 7 × 10.sup.19                                                                  0.25 0.8                           ______________________________________                                    

Referring now to FIG. 1b, a second photoresist masking layer 22 is thenpatterned on the first face 12a to expose a second portion thereof. Arelatively highly doped region of first conductivity type 20 (shown asN+) is then formed in the substrate 12, by implanting a firstconductivity type dopant 24 at the first face 12a. As will be understoodby those skilled in the art, a blanket implant of the first conductivitytype dopant can also be performed at the second face 12b to form asecond relatively highly doped region 26 (shown as N+). Alternatively,the silicon carbide substrate 12 can be formed by epitaxially growing anN-type layer on top of an N+ layer 26.

Referring now to FIG. 1c, first and second electrically conductive ohmiccontacts 32, 34 are then formed on the first and second relativelyhighly doped regions 20, 26, respectively. A rectifying Schottky gatecontact 30 can also be formed on the first face 12a, as illustrated, sothat the semiconductor device unit cell comprises ametal-epitaxial-semiconductor field effect transistor (MESFET) 10 havinga source 20, a lateral active region 15, a vertical active region 36 ordrift region which extends between the Schottky gate contact 30 and thesecond face 12b, and a relatively highly doped drain 26.

This MESFET 10 is a planar device which does not have a P-N junction inthe current path, between the source and drain regions 20, 26. Theforward blocking capability is achieved by the formation of a potentialbarrier between the source and drain regions. This can be done bydepletion of a thin silicon carbide active layer, between the Schottkygate contact 30 and the buried layer 18 either by the built-in potentialor by the application of a negative gate bias. A large drain voltage canbe supported by this structure because the drift region below the buriedlayer and the Schottky gate contact 30 becomes depleted. This driftregion supports most of the drain bias. The MESFET 10 also has a flybackdiode between the Schottky gate contact 30 and the drain 26, which canbe used with a silicon MOSFET (not shown) in series with the source.This and other applications of the present invention are described inthe aforementioned U.S. Pat. No. 5,396,085, entitled Silicon CarbideSwitching Device With Rectifying Gate, the disclosure of which is herebyincorporated herein by reference. The MESFET 10 also has high breakdownvoltage because the buried layer 18 can act as a guard ring for theSchottky gate contact 30. This reduces the electric field under theSchottky contact and prevents barrier lowering.

It will also be understood by those skilled in the art that multipleunit cells of the MESFET 10 of FIG. 1c can be electrically connected inparallel and integrated on a common silicon carbide substrate so thatarrays of cells can be paralleled for high current applications. Forexample, FIG. 2 illustrates a preferred layout of an integratedembodiment of the MESFET 10 of FIG. 1c, wherein the labelled regions A,B, C and D define the lateral extent of the first ohmic contact 32(source contact), first relatively highly doped region 20 (source),Schottky barrier gate contact 30 and buried layer 18, respectively. Thedistance "W_(o) " between adjacent buried layers 18 also defines asubstrate connecting region 38 of first conductivity type which connectsthe active layer 15 to the substrate. Thus, electrical carriers in theactive region 15 can be transferred to the substrate 12 and vice versawithout having to traverse the buried layer 18. Because the adjacentburied layers 18 are preferably formed simultaneously, they can betreated as a single buried layer having openings therein of width W_(o).

Referring now to FIG. 3a, the structure of a lateral siliconcarbide-on-insulator metal-oxide-semiconductor field effect transistor(MOSFET) 40, according to the present invention, will be described. TheMOSFET 40 preferably comprises a monocrystalline silicon carbide layer42 and an electrically insulating silicon carbide layer 44 on themonocrystalline silicon carbide layer 42. The electrically insulatingsilicon carbide layer 44 is preferably formed by performing one or moreblanket or selectively masked implants of electrically inactive ions sothat a relatively high resistance insulating layer is formed in thesubstrate beneath the face. The resistance is sufficient to provided ahigh degree of electrical isolation from the substrate. As describedabove, the electrically inactive ions are preferably selected from thegroup consisting of argon, neon, carbon and silicon. The MOSFET 40 alsoincludes a semiconducting silicon carbide active layer 46 on theelectrically insulating silicon carbide layer 44. This active layer 46can include source 48, drain 50 and channel regions 52 for anenhancement mode or depletion mode field effect transistor. Source anddrain ohmic contacts 54 and 56 are also formed on the respective sourceand drain regions 48 and 50. An insulated gate electrode 60 is alsopreferably provided by an electrically insulating layer 58 and aconductive gate electrode 59 thereon.

Referring now to FIG. 3b, the structure of a lateral siliconcarbide-on-insulator MESFET 40', according to the present invention, isillustrated. This MESFET 40' is similar to the MOSFET 40 of FIG. 3a,however, the insulated gate electrode 60 has been replaced with aSchottky barrier gate electrode 60' on the channel region 52.

In order to form a relatively thick electrically insulating siliconcarbide layer 44, multiple implant steps can also be performed insequence by varying, among other things, the implant energy of theelectrically inactive ions and/or the types of ions to be implanted. Inparticular, FIGS. 4a-b illustrate the implant distributions ofelectrically inactive ions such as He and C in silicon carbide atmultiple energies, respectively, and the combined profile ("Sum")resulting therefrom. If the dose (D₀) for the ion implantation step israised to a sufficient level ("D_(cr) "), an amorphous layer will format the peak of the implanted profile.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

That which is claimed is:
 1. A method of forming a silicon carbidesemiconductor device, comprising the steps of:implanting electricallyinactive ions selected from the group consisting of argon, neon, carbonand silicon into a face of a silicon carbide substrate of firstconductivity type to thereby form a silicon carbide buried layercontaining electrically active defects therein caused by the presence ofthe implanted electrically inactive ions at interstitial latticepositions, said buried layer being spaced from the face by a siliconcarbide active layer of first conductivity type and containing a greaterquantity of first conductivity type dopants therein than second oppositeconductivity type dopants and having a resistivity greater than aresistivity of the active layer; and forming at least one active regionof a silicon carbide semiconductor device in the active layer, betweensaid buried layer and the face.
 2. The method of claim 1, wherein saidimplanting step comprises implanting electrically inactive ions insufficient quantities so that said buried layer comprises anelectrically insulating layer having a resistivity greater than 10⁹Ohm-cm.
 3. The method of claim 2, wherein said implanting step ispreceded by the step of patterning a layer on the face of the substrate;and wherein said implanting step comprises implanting the electricallyinactive ions into the face using the patterned layer as an implant maskso that said buried layer contains an opening therein which electricallyconnects the active layer to the substrate.
 4. The method of claim 3,further comprising the step of forming a gate electrode on the face,opposite the opening.
 5. The method of claim 4, further comprising thesteps of forming a source region of first conductivity type in theactive layer, between said buried layer and the face; and forming adrain region of first conductivity type in the substrate, electricallycoupled to the opening in said buried layer.
 6. A method of forming asilicon carbide semiconductor device, comprising the steps of:forming asilicon carbide buried layer of second conductivity type beneath a faceof a silicon carbide substrate of first conductivity type, by implantingdopants of second conductivity type into the face so that said siliconcarbide buried layer is spaced from the face by an active layer of firstconductivity type, said silicon carbide buried layer having an openingtherein which electrically connects said silicon carbide active layer tosaid silicon carbide substrate; forming a first electrically conductivecontact on the face for providing charge carriers to and from saidsilicon carbide active layer; and forming a second electricallyconductive contact coupled to the opening in said silicon carbide buriedlayer.
 7. The method of claim 6, wherein said implanting step ispreceded by the step of patterning a layer on the face of the substrate;and wherein said implanting step comprises implanting the secondconductivity type dopants using the patterned layer as an implant maskto define the opening.
 8. The method of claim 7, further comprising thestep of forming a gate electrode on the face, opposite the opening. 9.The method of claim 8, further comprising the steps of forming a sourceregion of first conductivity type in the active layer, between saidburied layer and the face; and forming a drain region of firstconductivity type in the substrate, electrically coupled to the openingin said buried layer, so that the silicon carbide semiconductor devicecomprises a field effect transistor having source, drain and channelregions of first conductivity type.
 10. A method of forming a siliconcarbide semiconductor device, comprising the steps of:implanting ionsselected from a group consisting of second conductivity type dopants,argon, neon, carbon and silicon into a first face of a silicon carbidesubstrate of first conductivity type and at sufficient energies tothereby form a silicon carbide buried layer which contains the implantedions and is spaced from the first face by a silicon carbide active layerof first conductivity type through which the ions are implanted; andforming at least one active region of the silicon carbide semiconductordevice in the active layer, between the buried layer and the first face.11. The method of claim 10, wherein said implanting step comprisesimplanting ions at a sufficient dose so that the silicon carbide buriedlayer has a resistivity of greater than about 10⁹ Ohm-cm.
 12. The methodof claim 10, wherein the silicon carbide buried layer contains firstconductivity type dopants therein; and wherein the concentration offirst conductivity type dopants in the silicon carbide buried layerequals the concentration of first conductivity type dopants in thesilicon carbide active layer.
 13. The method of claim 11, wherein thesilicon carbide buried layer contains first conductivity type dopantstherein; and wherein the concentration of first conductivity typedopants in the silicon carbide buried layer equals the concentration offirst conductivity type dopants in the silicon carbide active layer. 14.The method of claim 10, wherein said implanting step is preceded by thestep of patterning a masking layer on the first face of the siliconcarbide substrate; and wherein said implanting step comprises implantingions into the first face of the silicon carbide substrate using thepatterned masking layer as an implant mask.
 15. The method of claim 14,wherein said implanting step comprises implanting ions into the firstface of the silicon carbide substrate using the patterned masking layeras an implant mask to thereby form a silicon carbide buried layer havingan opening therein which defines a substrate connecting region of firstconductivity type.
 16. The method of claim 15, further comprising thesteps of:forming a source region of first conductivity type in thesilicon carbide active layer; forming a drain region of firstconductivity type at a second face of the silicon carbide substrate,opposite the first face; and forming a gate electrode on the first face,opposite at least a portion of the silicon carbide buried layer.
 17. Themethod of claim 16, wherein said gate electrode forming step comprisesforming a gate electrode on the first face, opposite the opening in thesilicon carbide buried layer.
 18. The method of claim 10, furthercomprising the steps of:forming a source region of first conductivitytype in the silicon carbide active layer; forming a drain region offirst conductivity type at a second face of the silicon carbidesubstrate, opposite the first face; and forming a gate electrode on thefirst face, opposite at least a portion of the silicon carbide buriedlayer.
 19. The method of claim 10, further comprising the stepsof:forming a source region of first conductivity type in the siliconcarbide active layer; forming a drain region of first conductivity typein the silicon carbide active layer; and forming a gate electrode on thefirst face, opposite at least a portion of the silicon carbide buriedlayer.